The present invention relates to a semiconductor laser element and, more particularly, it relates to a multi-element or array type semiconductor laser device in which a plurality of laser elements is mounted on one substrate.
In conventional semiconductor laser elements, for example, as shown in FIG. 11, plural semiconductor laser portions 16 isolated electrically from each other by an isolation region 4 are formed in an array on the main surface of a semiconductor substrate 2 comprising GaAs and they are mounted on the device mounting region of the main surface of a sub-mount 21 with the main surface of the semiconductor substrate 2 pointing downwardly. On the element-mounting region of the sub-mount 21, plural electrodes 22 are disposed at positions opposite to respective electrodes 10 of the plural light emitting elements of the semiconductor laser elements. A solder layer 24 is then formed on the main surface of each of the plural electrodes 22. That is, the electrodes associated with the semiconductor laser elements are connected electrically mechanically by way of the solder layers 24 to the respective electrodes 22 on the element mounting region of the sub-mount.
On the region other than the element mounting region of the sub-mount, bonding pads 23 for connection with plural bonding wires are formed at such positions that the wires do not shield a laser beam upon attachment of the wires. The end sides of the bonding wires that are disposed to pass through the flanges of device packages are connected to the respective one end sides of a plurality of leads that are electrically isolated from the flanges, whereby the bonding wires can supply electric current to the element from the outside of the element package.
An object of this invention is to provide a semiconductor laser device with more improved yields in production than heretofore, as well as a manufacturing method thereof.
A specific subject of this invention is to provide a technique capable of preventing a short circuit between electrodes disposed side by side caused by soldering for fixing a semiconductor laser element and capable of improving yields in the assembling process of the array type semiconductor laser elements. The problems are to be explained below.
In the process for assembling the semiconductor laser elements described above, when each of the plural electrodes of the semiconductor laser elements is connected by way of a solder layer to each of plural electrodes disposed on an element mounting region of a sub-mount, a chip is pressed against heated molten solder under a pressure at a predetermined level or more. Therefore, pressure is generated in the molten solder layer. Such pressure is usually balanced with the surface tension of the molten solder at the end of a solder pattern. However, when a disturbing factor such as fine unevenness on the substrate surface or unevenness of solder pattern is present at the end of the solder pattern, the surface tension is weakened at the portion to cause the extrusion of the molten solder. The thus extruded molten solder is brought into contact with adjacent electrodes to cause a short circuit between adjacent electrodes to result in a problem that the yield is lowered in the process for assembling the semiconductor laser elements. In the prior art shown in FIG. 11, no effective countermeasure is taken against the pressure of such molten solder and the solder pattern may possibly be covered completely by the laser chip, so that it is necessary to additionally form a structure for preventing the extrusion of solder between laser stripes. In addition, the extrusion of solder is liable to be formed due to the refinement of the arrangement pitch in the semiconductor laser portion along with a size reduction and an increase of density of the semiconductor laser element and, on the other hand, the provision of the extrusion-preventive structure between the stripes increases the production cost, and occupies an extra area to result in a trouble for refinement.
A feature of this invention resides in a semiconductor laser having a semiconductor laser chip with a first electrode and a laser sustaining material, in which the laser sustaining material has an electrode and a solder layer in electrical connection therewith on a surface where the semiconductor laser chip is mounted, the first electrode of the semiconductor laser chip is connected with the solder layer of the laser sustaining material, and at least the solder layer of the laser sustaining material has a extended portion at the outside of an optical resonator of the semiconductor laser chip, the extended portion extending from at least one end face in the longitudinal direction of the optical resonator.
This invention is particularly effective when applied to a semiconductor laser element in which plural semiconductor laser portions isolated from each other by an isolation region are disposed in an array on a main surface of a semiconductor substrate, and each of plural electrodes is disposed on the main surface of each of the plural semiconductor laser portions, as well as a semiconductor laser device to which the semiconductor laser elements are assembled.
When the semiconductor chip is mounted on the laser sustaining material, the molten solder is guided to the solder layer extending to the outside of the optical resonator and the extrusion of the solder layer to the lateral side thereof can be prevented.
This invention is useful in a multi-element type or array type semiconductor laser device in which multiple elements are mounted on one substrate.
It is also important that the solder layer extending from at least one end face in the longitudinal direction of an optical resonator of the semiconductor laser element to the outside of the optical resonator is disposed so as to avoid the emitting position of a laser beam of the semiconductor laser element.
Furthermore, there may be considered various modes for the solder layer extending from at least one end face in the longitudinal direction of the optical resonator of the semiconductor laser element to the outside of the optical resonator. A typically mode has the extended portion in at least one of the right and left sides relative to the longitudinal direction of the optical resonator of the semiconductor laser element, and the extended portion of the solder layer is present at, at lest one of the front end and the back end of the optical resonator. It is of course possible to provide the extended portion of the semiconductor layer at both the right and left sides relative to the longitudinal direction of the optical resonator, or at both the front end and the back end of the optical resonator.
Further, in a case where the number of the plural semiconductor laser portions arranged in an array is three or more, it is preferred that the semiconductor laser portions excluding the two semiconductor laser portions on both ends of the disposed semiconductor laser portions are constituted in the modes of the invention.
According to the means described above, in the process for assembling the semiconductor laser elements, when each of plural electrodes of the semiconductor laser elements is connected by way of the solder layer to each of plural electrodes disposed on the element mounting region of the sub-mount respectively, since solder discharged by pressing the laser chip is allowed to escape in the extending direction of the stripe, a short circuit between adjacent electrodes can be prevented. As a result, the yield in the process for assembling the semiconductor laser elements can be enhanced.
Further, this invention can provide a semiconductor laser element capable of preventing a short circuit between electrodes caused by extruded solder and capable of improving the yield in the process for assembling the semiconductor laser elements.